Edema is an abnormal accumulation of fluid in the interstitium, located beneath the skin and in the cavities of the body. Clinically, edema is manifest as swelling. The amount of interstitial fluid is determined by the balance of fluid homeostasis; increased secretion of fluid into the interstitium, or the impaired removal of the fluid can cause edema. The more the fluid accumulates, the more the tissue swells, resulting in decreased blood flow in the blood vessels of the dermis. Although edema can occur anywhere in the body, it is most commonly seen in the ankles, feet, and legs.
The skin is the largest organ in the body and it acts as the first line of defense against environmental factors. The skin has multiple layers. The stratum corneum is the outermost layer of the skin and forms part of the epidermis. The dermis, which is underneath the epidermis, is mainly composed of capillaries and lymph vessels. Skin thickness varies. The epidermis is only 0.05 mm thick on the eyelids, but is 1.5 mm thick on the palms and the soles of the feet. Thickness of the dermis varies from 1.5 mm to 4 mm.
Normally the hydrostatic pressure of a capillary is about 35 mmHg in the arteriole and 18 mmHg in the venule [1]. The normal osmotic pressure of a capillary is 25 mmHg for both arterioles and venules [1]. Disruption of these pressures alters the osmotic balance, consequently causing edema. Other common causes of edema include decreased plasma proteins, increased capillary permeability, and blockage of the lymphatic system.
Lymphedema is an abnormal accumulation of lymphatic fluid in the interstitial tissue that causes swelling, most often in the arm(s) and/or leg(s) and occasionally in other parts of the body due to a compromised lymphatic system. The lymphatic system is composed of a network of lymph vessels (some of which are found in the dermis), tissues, and organs that transport lymph fluid throughout the whole body. It also collects and filters the interstitial fluid of the body. In addition, the lymphatic system prepares the body for when it is time to fight an infection or disease.
Proper function of the lymphatic system is critical for a healthy individual. Normally, lymph is transported throughout the body and delivered back to the bloodstream; however, when the lymphatic system is blocked or damaged, the fluid is not drained from the tissues. As a consequence, an abnormal accumulation of extracellular fluid occurs, leading to excessive swelling of the tissue. As the fluid accumulation increases and the tissue swells, the pressure build-up in the affected limb causes a decrease in blood flow.
There are two types of lymphedema: primary or secondary. Primary lymphedema occurs when a person is born with an abnormal lymphatic system. Secondary lymphedema occurs when lymph vessels are damaged or lymph nodes are removed due to certain factors, such as radiation, burns, tumors, infections, and/or trauma. In the United States, the most common cause of secondary lymphedema is breast cancer surgery combined with radiation therapy [10-12].
Surgery and/or treatment for prostate, colon and testicular cancers may result in secondary lymphedema, particularly where lymph nodes have been removed or damaged.
When a patient has chronic lymphedema, some of the most prominent skin changes that arise as the condition progresses include papillomatosis, lymphangiectasia, and hyperkeratosis. There are certain inflammatory conditions that may contribute to lymphedema development, including sarcoidosis, rheumatoid arthritis, and psoriasis. Some cases of patients with acne vulgaris and rosacea have developed lymphedema in the face. Certain patients who have suffered from a form of trauma, such as varicose vein surgery and radiotherapy, have also developed lymphedema due to the damage caused to their lymphatic system. Finally, patients with venous disease are predisposed to lymphedema because of the increased capillary filtration and the incompetence of the lymphatic system
When the impairment becomes so great that the lymphatic fluid exceeds the lymphatic transport capacity, an abnormal amount of protein-rich fluid collects in the tissues of the affected area. Left untreated, this stagnant, protein-rich fluid not only causes tissue channels to increase in size and number, but also reduces oxygen availability in the transport system, interferes with wound healing, and provides a culture medium for bacteria that can result in lymphangitis (infection). Symptoms may include severe fatigue, a heavy swollen limb or localized fluid accumulation in other body areas, deformity (“elephantiasis”), discoloration of the skin overlying the lymphedema, recurrent episodes of cellulitis, and in severe cases, skin ulcers and infections.
Lymphedema may also result in psychological distress. The normal, daily-living lifestyle can become severely limited. A treatment for lymphedema is called Complete Decongestive Therapy, which may include manual lymphatic drainage, compression therapy, short stretch compression bandaging, therapeutic exercise, and skin care.
Lymphedema affects approximately 140 million people in the world and approximately 5 million people in the United States. In addition, out of the 2.5 million breast cancer survivors, lymphedema occurs in 40% of those patients because cancer treatment damages the patients' lymphatic system. Currently, there is no technology that offers patients an understanding of what actions may aggravate their conditions or that aids in managing lymphedema.
Therefore, the ability to gain insights into, and/or monitor, this disease and its progression are of great interest.